1. Field of the Invention
The present invention relates to a method of removing vinyl chloride monomer which remains in a polymer. More particularly, it relates to a method of removing vinyl chloride monomer which remains in a polymer of vinyl chloride such as vinyl chloride homo- or copolymers.
2. Description of the Prior Art
Recently, the toxicity of vinyl chloride to the human body has become a serious problem. It has been required by government agencies that the escape of vinyl chloride monomer in processes for producing a polymer of vinyl chloride be prevented. It has been required that the vinyl chloride monomer which remains in the product polymer of vinyl chloride be reduced as much as possible from the viewpoint of the characteristics of the products when processing the polymer and also for the health of the operators. In order to remove the vinyl chloride monomer which remains in a polymer of vinyl chloride, various processes have been carried out. For example, removing the vinyl chloride monomer by stirring a slurry of the polymerization mixture under reduced pressure after the polymerization or by removing the vinyl chloride monomer which remains in the polymer by heating the polymer have been employed.
However, these methods have the disadvantages of low efficiency for removing vinyl chloride monomer or deterioration of the desirable characteristics of the polymer. It has been proposed to heat the polymer for a short time while maintaining a layer of water on the surface of the polymer in order to prevent the deterioration of the polymer while the vinyl chloride monomer is removed by the heating operation. However, this method is not very efficient even though the deterioration of the polymer can be prevented to a degree.
Accordingly, there is a need for a method of removing vinyl chloride monomer from a polymer with good efficiency and without deterioration of the polymer properties.